The present invention relates to vehicles including motor vehicles and towed vehicles in which the vehicle is provided with a load receiving tray or bed which is movable from a raised transport position to a lowered position at which the bed is located adjacent ground level to facilitate loading and unloading.
U.S. Pat. No. 5,035,462 describes a motor vehicle having a chassis provided with a cab, and a rear assembly including a vertically movable load receiving bed, which is movable between an upper transport position and lower position located substantially at ground level. Inventive improvements on this vehicle are descrbked in International Publication No. WO 96/34778 (from International Application No. PCT/AU96/00255) and in International Publication No. WO 98/07591 (from International Application No. PCT/AU97/00523). In these vehicles, mechanical linkage systems are employed to raise and lower the load receiving bed.
As provided by this invention, a vehicle assembly includes a chassis of generally xe2x80x9cUxe2x80x9d shaped configuration so as to provide a generally horizontal transverse base from which there rearwardly extends a pair of legs, and load receiving bed supported between the legs and movable between a raised transport position and a lowered position against a surface upon which the vehicle is resting.
Moreover, the vehicle assembly includes a pair of forward hydraulic cylinders spaced on opposite sides of the load receiving bed and operatively extending between the chassis and the load receiving bed and a pair of rearward hydraulic cylinders located on opposite sides of the load receiving bed and operatively extending between rear portions of the legs and the load receiving bed, wherein the four cylinders support the bed in the raised and lowered positions and are arranged in series one to four. Each cylinder has a rod providing a swept volume. The swept volumes are arranged so that the rods move in unison. Each cylinder has a rod end and a non-rod end. The cylinders are connected so that fluid flows between a rod end and a non-rod end of adjacently connected cylinders.
Furthermore, the vehicle assembly includes hydraulic means to deliver hydraulic fluid under pressure to the hydraulic cylinders to raise and lower the load receiving bed, which means include a pump to provide hydraulic fluid under pressure, a control valve, a flow restriction device, a first hydraulic line extending to the first cylinder, a second hydraulic line extending from the fourth cylinder, and a third hydraulic line extending from the valve to take hydraulic fluid from the valve. The control valve is connected to the pump to coordinate movement of hydraulic fluid to and from the cylinders. In a first operative position, the control valve connects the first hydraulic line to the pump and connects the second hydraulic line to the pump, thereby to raise the bed. In a second operative position, the control valve connects the second hydraulic line to the pump and connects the first hydraulic line to the third hydraulic line, thereby to lower the bed. The flow restriction device is operable to govern the speed at which the bed is lowered.
Preferably, the flow restriction device is located in the second hydraulic line. Preferably, the vehicle assembly further includes a one way valve arranged in parallel with respect to the flow restriction device, the one way valve providing for the flow of hydraulic fluid from the control valve to the first cylinder.
In a preferred embodiment of this invention, the vehicle assembly further includes forward catch means to engage the load receiving bed in the transport position but releasable to permit movement of the load receiving bed and the vehicle assembly further includes a tailgate pivotally attached to a rear portion of the load receiving bed and moveable with the load receiving bed between the raised and lowered positions thereof, wherein the tailgate is pivotally movable between a generally upright position extending between the legs and a lowered position extending rearwardly from the receiving bed, when lowered, to provide for access to the receiving bed, when lowered, and wherein the tailgate engages the legs to aid in vertically supporting the load receiving bed, when raised.